With an increased focus on green energy production in recent years, more wind turbines or windmills are being installed to harness wind energy. Many modern wind turbines include blades having lengths in the range of about twenty-five (25) meters (m) to about ninety-nine (99) m. Furthermore, such blades are rotatably mounted on a mast whose height may range from about eighty (80) m to about one hundred and twenty (120) m. During conditions where sufficient wind is present to turn the blades, the blades rotate a turbine attached to an electric generator to create electrical power. This power may be used to supply additional electric power to the distribution grid, or may be used directly by the wind turbine owner. As the demand for renewable energy sources increases, the need for a greater number of wind turbines will increase. Multiple wind turbines are sometimes installed across expansive open areas grouped in wind farms to harness the power of the wind and convert it to electrical energy.
Ground based radars are a primary source of information regarding atmospheric conditions, location and quantity of water and/or ice, as well as other objects in the atmosphere. Existing ground based radar applications must meet certain criteria such as coverage, accuracy, latency, scan rate, reliability and resolution. Currently, ground based radars serve as a key component of national surveillance systems that detect and track objects operating in the nation's airspace. In addition to applications in the defense industry, radar fulfills various civilian requirements. These civilian applications include but are not limited to air traffic control, weather surveillance and tracking, tracking airborne releases of toxic materials, calibration of satellite-based instruments, observing debris flow from disasters such as mudslides and floods, monitoring air quality, monitoring movement of volcanic ash, and detecting birds and other aviation hazards.
Radar operates within its line of sight. Electromagnetic radio frequency waves are transmitted by a radar sensor configured to transmit and receive the electromagnetic waves. The waves propagate through the air until they contact an object. When the waves are impinged by an object, the waves are reflected back toward the transmission source. The radar sensor receives the reflected echo waves. Based on the time it takes for the wave to travel to the object and be reflected back to the sensor, the round trip time of the wave may be calculated based on the speed of the electromagnetic wave, which is substantially equal to the speed of light.
Doppler radar is used to detect objects which are moving with respect to the object's background. For example, Doppler radar is effective for tracking storm systems as they move across a terrain. Doppler radar determines the range and velocity of a target object based on the Doppler effect. As the electromagnetic waves of the radar impinge a moving target, the frequency of the echo (reflected) wave is altered based on the object's direction and speed of motion. For example, an object approaching a radar sensor generates a reflected wave at a frequency higher than that of the transmitted wave. An object moving away from the radar sensor generates a reflected wave at a frequency lower than the transmitted wave.
Wind turbines interfere with radar, particularly Doppler radar because of the time variable signatures generated by the rotating blades. The interference caused by wind turbines creates blind spots in the radar coverage when a wind turbine is installed in the line of sight of the radar installation. In the interest of national security, permission to install wind turbines in the line of sight of existing radar installations may be prohibited. Other remediation actions include additional processing intended to filter the wind turbine signature. However, such techniques risk corrupting the received data signal and may increase the likelihood that a threat will go undetected. Additionally, complex processing taxes the computer's resources and timelines available in existing legacy radar systems. Additional air traffic rules may be implemented in areas near or above wind turbines. However, such measures do not address the situation where an airborne object does not comply with air traffic regulations.
Improved radar systems that are not adversely affected by wind turbines are desired.